1. Field of the Invention
The present invention relates to a vibrational wave motor, a lens barrel and camera.
2. Related Art
In a vibrational wave motor, a progressive oscillating wave (hereinafter abbreviated as progressive wave) is generated at the driving face of an elastic body using the expansion and contraction of a piezoelectric body. Further, an elliptic motion arises at the driving face by the progressive wave, and a moving element in pressure contact with the wave crests of the elliptic movement is driven (for example, refer to Japanese Examined Patent Publication No. H1-17354).
Such a vibrational wave motor is characterized in having high torque even at low rotation rates, thus when mounted on a driving device, it is possible to reduce the number of gears of the driving device. Therefore, the noise generated by the gears can be reduced, and it is possible to achieve a reduction in sound, and further, the positioning accuracy can be improved.
In recent years, there has been a trend to lighten and miniaturize vibrational wave motors such that the diameter is about ⅓ to ⅕ of those of the prior art. Such a miniaturized vibrational wave motor, which has good ease of use for inclusion in machinery, has advanced applicability for a wide range of applications. Accordingly, the number being shipped is greatly increasing.
In such a vibrational wave motor, a pressure is applied such that a driving force is transmitted between the driving face of the elastic body and the sliding face of the moving element to which the driving force is transmitted from the driving face. In the prior art, this pressing force has been generated by a spring member into which an output shaft is inserted (for example, refer to Japanese Unexamined Patent Publication No. 2006-333629). Therefore, there had been limitations to the shortening of the length in a direction of the output shaft of the vibrational wave motor.
On the other hand, the constitution of a vibrational wave motor has been disclosed where, one part for generating a pressing force is disposed more radially outside than another part where an elastic body and a moving element are disposed, without the one part being disposed centered about an output shaft, (for example, refer to Japanese Unexamined Patent Publication No. H11-196591).
However, a pressing force generated in Japanese Unexamined Patent Publication No. H11-196591 is inclined and not parallel to the output shaft. Accordingly, it gives rise to drawbacks that since the pressing force between an oscillator and the moving element is offset, an unpleasant sound is generated at high rotation rates, the driving efficiency is reduced, and the generation of a high load is difficult, and the like.